Recently, development of an optical wiring board in which part of electrical wires is replaced by optical wires such as optical waveguides is considered. In particular, use of optical waveguides among optical wires is considered because the degree of freedom in designing the shape is higher than that of optical fibers and integrated formation with a conventional electrical wiring board is possible.
For example, optical wiring boards disclosed in Japanese Unexamined Patent Publications JP-A 2000-298216 and JP-A 2004-54003 internally include a core portion that transmits light. Photoelectric conversion elements such as a light-emitting device and a light-receiving device are used for converting signals between the optical wires and the electrical wires.
Furthermore, for example, in a wiring board disclosed in Unexamined Patent Publication JP-A 1-179501 (1989) as an electrical wiring board that operates at a high speed, a pair of differential lines are arranged inside the wiring board with a predetermined gap interposed therebetween in the thickness direction.
However, the optical wires and the electrical wires are arranged in different layers in conventional examples, and, thus, the thickness of the optical-electrical wiring board tends to be large.